NVO3 Workgroup                                           J. Rabadan, Ed.
Internet-Draft                                                  M. Bocci
Intended status: Informational                                     Nokia
Expires: 23 December 2022                                     S. Boutros
                                                                   Ciena
                                                              A. Sajassi
                                                                   Cisco
                                                            21 June 2022


                 Applicability of EVPN to NVO3 Networks
                 draft-ietf-nvo3-evpn-applicability-04

Abstract

   In NVO3 networks, Network Virtualization Edge (NVE) devices sit at
   the edge of the underlay network and provide Layer-2 and Layer-3
   connectivity among Tenant Systems (TSes) of the same tenant.  The
   NVEs need to build and maintain mapping tables so that they can
   deliver encapsulated packets to their intended destination NVE(s).
   While there are different options to create and disseminate the
   mapping table entries, NVEs may exchange that information directly
   among themselves via a control-plane protocol, such as Ethernet
   Virtual Private Network (EVPN).  EVPN provides an efficient, flexible
   and unified control-plane option that can be used for Layer-2 and
   Layer-3 Virtual Network (VN) service connectivity.  This document
   describes the applicability of EVPN to NVO3 networks and how EVPN
   solves the challenges in those networks.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 23 December 2022.






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Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  EVPN and NVO3 Terminology . . . . . . . . . . . . . . . . . .   3
   3.  Why is EVPN Needed in NVO3 Networks?  . . . . . . . . . . . .   6
   4.  Applicability of EVPN to NVO3 Networks  . . . . . . . . . . .   8
     4.1.  EVPN Route Types Used in NVO3 Networks  . . . . . . . . .   8
     4.2.  EVPN Basic Applicability for Layer-2 Services . . . . . .   9
       4.2.1.  Auto-Discovery and Auto-Provisioning  . . . . . . . .  10
       4.2.2.  Remote NVE Auto-Discovery . . . . . . . . . . . . . .  12
       4.2.3.  Distribution of Tenant MAC and IP Information . . . .  12
     4.3.  EVPN Basic Applicability for Layer-3 Services . . . . . .  13
     4.4.  EVPN as Control Plane for NVO3 Encapsulations and
           GENEVE  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     4.5.  EVPN OAM and Application to NVO3  . . . . . . . . . . . .  16
     4.6.  EVPN as the Control Plane for NVO3 Security . . . . . . .  16
     4.7.  Advanced EVPN Features for NVO3 Networks  . . . . . . . .  16
       4.7.1.  Virtual Machine (VM) Mobility . . . . . . . . . . . .  16
       4.7.2.  MAC Protection, Duplication Detection and Loop
               Protection  . . . . . . . . . . . . . . . . . . . . .  17
       4.7.3.  Reduction/Optimization of BUM Traffic in Layer-2
               Services  . . . . . . . . . . . . . . . . . . . . . .  17
       4.7.4.  Ingress Replication (IR) Optimization for BUM
               Traffic . . . . . . . . . . . . . . . . . . . . . . .  18
       4.7.5.  EVPN Multi-Homing . . . . . . . . . . . . . . . . . .  19
       4.7.6.  EVPN Recursive Resolution for Inter-Subnet Unicast
               Forwarding  . . . . . . . . . . . . . . . . . . . . .  20
       4.7.7.  EVPN Optimized Inter-Subnet Multicast Forwarding  . .  21
       4.7.8.  Data Center Interconnect (DCI)  . . . . . . . . . . .  21
   5.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . .  22
   6.  Conventions Used in this Document . . . . . . . . . . . . . .  22
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  22
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  23



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     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  23
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  23
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  27
   Appendix B.  Contributors . . . . . . . . . . . . . . . . . . . .  27
   Appendix C.  Authors' Addresses . . . . . . . . . . . . . . . . .  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

1.  Introduction

   In NVO3 networks, Network Virtualization Edge (NVE) devices sit at
   the edge of the underlay network and provide Layer-2 and Layer-3
   connectivity among Tenant Systems (TSes) of the same tenant.  The
   NVEs need to build and maintain mapping tables so that they can
   deliver encapsulated packets to their intended destination NVE(s).
   While there are different options to create and disseminate the
   mapping table entries, NVEs may exchange that information directly
   among themselves via a control-plane protocol, such as EVPN.  EVPN
   provides an efficient, flexible and unified control-plane option that
   can be used for Layer-2 and Layer-3 Virtual Network (VN) service
   connectivity.

   In this document, we assume that the EVPN control-plane module
   resides in the NVEs.  The NVEs can be virtual switches in
   hypervisors, TOR/Leaf switches or Data Center Gateways.  As described
   in [RFC7365], Network Virtualization Authorities (NVAs) may be used
   to provide the forwarding information to the NVEs, and in that case,
   EVPN could be used to disseminate the information across multiple
   federated NVAs.  The applicability of EVPN would then be similar to
   the one described in this document.  However, for simplicity, the
   description assumes control-plane communication among NVE(s).

2.  EVPN and NVO3 Terminology

   *  AC: Attachment Circuit or logical interface associated to a given
      BT.  To determine the AC on which a packet arrived, the NVE will
      examine the physical/logical port and/or VLAN tags (where the VLAN
      tags can be individual c-tags, s-tags or ranges of both).

   *  ARP and ND: Address Resolution Protocol and Neighbor Discovery
      protocol.

   *  BD: or Broadcast Domain, it corresponds to a tenant IP subnet.  If
      no suppression techniques are used, a BUM frame that is injected
      in a BD will reach all the NVEs that are attached to that BD.  An
      EVI may contain one or multiple BDs depending on the service model
      [RFC7432].  This document will use the term BD to refer to a
      tenant subnet.




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   *  BT: a Bridge Table, as defined in [RFC7432].  A BT is the
      instantiation of a BD in an NVE.  When there is a single BD on a
      given EVI, the MAC-VRF is equivalent to the BT on that NVE.

   *  BUM: Broadcast, Unknown unicast and Multicast frames.

   *  CLOS: a multistage network topology described in [CLOS1953], where
      all the edge switches (or Leafs) are connected to all the core
      switches (or Spines).  Typically used in Data Centers nowadays.

   *  DF and NDF: they refer to Designated Forwarder and Non-Designated
      Forwarder, which are the roles that a given PE can have in a given
      ES.

   *  ECMP: Equal Cost Multi-Path.

   *  EVPN: Ethernet Virtual Private Networks, as described in
      [RFC7432].

   *  EVPN VLAN-based service model: one of the three service models
      defined in [RFC7432].  It is characterized as a BD that uses a
      single VLAN per physical access port to attach tenant traffic to
      the BD.  In this service model, there is only one BD per EVI.

   *  EVPN VLAN-bundle service model: similar to VLAN-based but uses a
      bundle of VLANs per physical port to attach tenant traffic to the
      BD.  As in VLAN-based, in this model there is a single BD per EVI.

   *  EVPN VLAN-aware bundle service model: similar to the VLAN-bundle
      model but each individual VLAN value is mapped to a different BD.
      In this model there are multiple BDs per EVI for a given tenant.
      Each BD is identified by an "Ethernet Tag", that is a control-
      plane value that identifies the routes for the BD within the EVI.

   *  ES: Ethernet Segment.  When a Tenant System (TS) is connected to
      one or more NVEs via a set of Ethernet links, then that set of
      links is referred to as an 'Ethernet segment'.  Each ES is
      represented by a unique Ethernet Segment Identifier (ESI) in the
      NVO3 network and the ESI is used in EVPN routes that are specific
      to that ES.











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   *  Ethernet Tag: Used to represent a BD that is configured on a given
      ES for the purpose of DF election.  Note that any of the following
      may be used to represent a BD: VIDs (including Q-in-Q tags),
      configured IDs, VNIs (Virtual Extensible Local Area Network
      (VXLAN) Network Identifiers), normalized VIDs, I-SIDs (Service
      Instance Identifiers), etc., as long as the representation of the
      BDs is configured consistently across the multihomed PEs attached
      to that ES.  The Ethernet Tag value MUST be different from zero.

   *  EVI: or EVPN Instance.  It is a Layer-2 Virtual Network that uses
      an EVPN control-plane to exchange reachability information among
      the member NVEs.  It corresponds to a set of MAC-VRFs of the same
      tenant.  See MAC-VRF in this section.

   *  GENEVE: Generic Network Virtualization Encapsulation, an NVO3
      encapsulation defined in [RFC8926].

   *  IP-VRF: an IP Virtual Routing and Forwarding table, as defined in
      [RFC4364].  It stores IP Prefixes that are part of the tenant's IP
      space, and are distributed among NVEs of the same tenant by EVPN.
      Route-Distinghisher (RD) and Route-Target(s) (RTs) are required
      properties of an IP-VRF.  An IP-VRF is instantiated in an NVE for
      a given tenant, if the NVE is attached to multiple subnets of the
      tenant and local inter-subnet-forwarding is required across those
      subnets.

   *  IRB: Integrated Routing and Bridging interface.  It refers to the
      logical interface that connects a BD instance (or a BT) to an IP-
      VRF and allows to forward packets with destination in a different
      subnet.

   *  MAC-VRF: a MAC Virtual Routing and Forwarding table, as defined in
      [RFC7432].  The instantiation of an EVI (EVPN Instance) in an NVE.
      Route-distinghisher (RD) and Route-Target(s) (RTs) are required
      properties of a MAC-VRF and they are normally different than the
      ones defined in the associated IP-VRF (if the MAC-VRF has an IRB
      interface).

   *  NVE: Network Virtualization Edge is a network entity that sits at
      the edge of an underlay network and implements L2 and/or L3
      network virtualization functions.  The network-facing side of the
      NVE uses the underlying L3 network to tunnel tenant frames to and
      from other NVEs.  The tenant-facing side of the NVE sends and
      receives Ethernet frames to and from individual Tenant Systems.
      In this document, an NVE could be implemented as a virtual switch
      within a hypervisor, a switch or a router, and runs EVPN in the
      control-plane.




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   *  NVO3 or Overlay tunnels: Network Virtualization Over Layer-3
      tunnels.  In this document, NVO3 tunnels or simply Overlay tunnels
      will be used interchangeably.  Both terms refer to a way to
      encapsulate tenant frames or packets into IP packets whose IP
      Source Addresses (SA) or Destination Addresses (DA) belong to the
      underlay IP address space, and identify NVEs connected to the same
      underlay network.  Examples of NVO3 tunnel encapsulations are
      VXLAN [RFC7348], GENEVE [RFC8926] or MPLSoUDP [RFC7510].

   *  PE: Provider Edge router.

   *  PTA: Provider Multicast Service Interface Tunnel Attribute.

   *  RT and RD: Route Target and Route Distinguisher.

   *  RT-1, RT-2, RT-3, etc.: they refer to Route Type followed by the
      type number as defined in the IANA registry for EVPN route types.

   *  SA and DA: Source Address and Destination Address.  They are used
      along with MAC or IP, e.g.  IP SA or MAC DA.

   *  SBD: Supplementary Broadcast Domain.  Defined in [RFC9136], it is
      a BD that does not have any ACs, only IRB interfaces, and provides
      connectivity among all the IP-VRFs of a tenant in the Interface-
      ful IP-VRF-to-IP-VRF models.

   *  TS: Tenant System.

   *  VNI: Virtual Network Identifier.  Irrespective of the NVO3
      encapsulation, the tunnel header always includes a VNI that is
      added at the ingress NVE (based on the mapping table lookup) and
      identifies the BT at the egress NVE.  This VNI is called VNI in
      VXLAN or GENEVE, VSID in nvGRE or Label in MPLSoGRE or MPLSoUDP.
      This document will refer to VNI as a generic Virtual Network
      Identifier for any NVO3 encapsulation.

   *  VXLAN: Virtual eXtensible Local Area Network, an NVO3
      encapsulation defined in [RFC7348].

3.  Why is EVPN Needed in NVO3 Networks?

   Data Centers have adopted NVO3 architectures mostly due to the issues
   discussed in [RFC7364].  The architecture of a Data Center is
   nowadays based on a CLOS design, where every Leaf is connected to a
   layer of Spines, and there is a number of ECMP paths between any two
   leaf nodes.  All the links between Leaf and Spine nodes are routed
   links, forming what we also know as an underlay IP Fabric.  The
   underlay IP Fabric does not have issues with loops or flooding (like



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   old Spanning Tree Data Center designs did), convergence is fast and
   ECMP provides a fairly optimal bandwidth utilization on all the
   links.

   On this architecture and as discussed by [RFC7364] multi-tenant
   intra-subnet and inter-subnet connectivity services are provided by
   NVO3 tunnels, being VXLAN [RFC7348] or GENEVE [RFC8926] two examples
   of such tunnels.

   Why is a control-plane protocol along with NVO3 tunnels required?
   There are three main reasons:

   a.  Auto-discovery of the remote NVEs that are attached to the same
       VPN instance (Layer-2 and/or Layer-3) as the ingress NVE is.

   b.  Dissemination of the MAC/IP host information so that mapping
       tables can be populated on the remote NVEs.

   c.  Advanced features such as MAC Mobility, MAC Protection, BUM and
       ARP/ND traffic reduction/suppression, Multi-homing, Prefix
       Independent Convergence (PIC) like functionality, Fast
       Convergence, etc.

   A possible approach to achieve points (a) and (b) above for
   multipoint Ethernet services, is "flood and learn".  "Flood and
   learn" refers to not using a specific control-plane on the NVEs, but
   rather "flood" BUM traffic from the ingress NVE to all the egress
   NVEs attached to the same BD.  The egress NVEs may then use data path
   MAC SA "learning" on the frames received over the NVO3 tunnels.  When
   the destination host replies back and the frames arrive at the NVE
   that initially flooded BUM frames, the NVE will also "learn" the MAC
   SA of the frame encapsulated on the NVO3 tunnel.  This approach has
   the following drawbacks:

   *  In order to flood a given BUM frame, the ingress NVE must know the
      IP addresses of the remote NVEs attached to the same BD.  This may
      be done as follows:

      -  The remote tunnel IP addresses can be statically provisioned on
         the ingress NVE.  If the ingress NVE receives a BUM frame for
         the BD on an ingress AC, it will do ingress replication and
         will send the frame to all the configured egress NVE IP DAs in
         the BD.

      -  All the NVEs attached to the same BD can subscribe to an
         underlay IP Multicast Group that is dedicated to that BD.  When
         an ingress NVE receives a BUM frame on an ingress AC, it will
         send a single copy of the frame encapsulated into an NVO3



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         tunnel, using the multicast address as IP DA of the tunnel.
         This solution requires PIM in the underlay network and the
         association of individual BDs to underlay IP multicast groups.

   *  "Flood and learn" solves the issues of auto-discovery and learning
      of the MAC to VNI/tunnel IP mapping on the NVEs for a given BD.
      However, it does not provide a solution for advanced features and
      it does not scale well (mostly due to the need for constant
      flooding and the underlay PIM states that are needed to maintain).

   EVPN provides a unified control-plane that solves the NVE auto-
   discovery, tenant MAP/IP dissemination and advanced features in a
   scalable way and keeping the independence of the underlay IP Fabric,
   i.e., there is no need to enable PIM in the underlay network and
   maintain multicast states for tenant BDs.

   Section 4 describes how EVPN can be used to meet the control-plane
   requirements in an NVO3 network.

4.  Applicability of EVPN to NVO3 Networks

   This section discusses the applicability of EVPN to NVO3 networks.
   The intend is not to provide a comprehensive explanation of the
   protocol itself but give an introduction and point at the
   corresponding reference document, so that the reader can easily find
   more details if needed.

4.1.  EVPN Route Types Used in NVO3 Networks

   EVPN supports multiple Route Types and each type has a different
   function.  For convenience, Table 1 shows a summary of all the
   existing EVPN route types and its usage.  We will refer to these
   route types as RT-x routes throughout the rest of the document, where
   x is the type number included in the first column of Table 1.

















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   +======+=====================+======================================+
   | Type | Description         | Usage                                |
   +======+=====================+======================================+
   | 1    | Ethernet Auto-      | Multi-homing: Per-ES: Mass           |
   |      | Discovery           | withdrawal, Per-EVI: aliasing/backup |
   +------+---------------------+--------------------------------------+
   | 2    | MAC/IP              | Host MAC/IP dissemination, supports  |
   |      | Advertisement       | MAC mobility and protection          |
   +------+---------------------+--------------------------------------+
   | 3    | Inclusive           | NVE discovery and BUM flooding tree  |
   |      | Multicast           | setup                                |
   |      | Ethernet Tag        |                                      |
   +------+---------------------+--------------------------------------+
   | 4    | Ethernet            | Multi-homing: ES auto-discovery and  |
   |      | Segment             | DF Election                          |
   +------+---------------------+--------------------------------------+
   | 5    | IP Prefix           | IP Prefix dissemination              |
   +------+---------------------+--------------------------------------+
   | 6    | Selective           | Indicate interest for a multicast    |
   |      | Multicast           | S,G or *,G                           |
   |      | Ethernet Tag        |                                      |
   +------+---------------------+--------------------------------------+
   | 7    | Multicast Join      | Multi-homing: S,G or *,G state synch |
   |      | Synch               |                                      |
   +------+---------------------+--------------------------------------+
   | 8    | Multicast           | Multi-homing: S,G or *,G leave synch |
   |      | Leave Synch         |                                      |
   +------+---------------------+--------------------------------------+
   | 9    | Per-Region          | BUM tree creation across regions     |
   |      | I-PMSI A-D          |                                      |
   +------+---------------------+--------------------------------------+
   | 10   | S-PMSI A-D          | Multicast tree for S,G or *,G states |
   +------+---------------------+--------------------------------------+
   | 11   | Leaf A-D            | Used for responses to explicit       |
   |      |                     | tracking                             |
   +------+---------------------+--------------------------------------+

                         Table 1: EVPN route types

4.2.  EVPN Basic Applicability for Layer-2 Services

   Although the applicability of EVPN to NVO3 networks spans multiple
   documents, EVPN's baseline specification is [RFC7432].  [RFC7432]
   allows multipoint layer-2 VPNs to be operated as [RFC4364] IP-VPNs,
   where MACs and the information to setup flooding trees are
   distributed by MP-BGP [RFC4760].  Based on [RFC7432], [RFC8365]
   describes how to use EVPN to deliver Layer-2 services specifically in
   NVO3 Networks.



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   Figure 1 represents a Layer-2 service deployed with an EVPN BD in an
   NVO3 network.

                                 +--TS2---+
                                 *        | Single-Active
                                 *        |   ESI-1
                               +----+  +----+
                               |BD1 |  |BD1 |
                 +-------------|    |--|    |-----------+
                 |             +----+  +----+           |
                 |              NVE2    NVE3          NVE4
                 |           EVPN NVO3 Network       +----+
            NVE1(IP-A)                               | BD1|-----+
           +-------------+      RT-2                 |    |     |
           |             |    +-------+              +----+     |
           |   +----+    |    |MAC1   |               NVE5     TS3
    TS1--------|BD1 |    |    |IP1    |              +----+     |
    MAC1   |   +----+    |    |Label L|--->          | BD1|-----+
    IP1    |             |    |NH IP-A|              |    | All-Active
           | Hypervisor  |    +-------+              +----+  ESI-2
           +-------------+                              |
                 +--------------------------------------+

             Figure 1: EVPN for L2 in an NVO3 Network - example

   In a simple NVO3 network, such as the example of Figure 1, these are
   the basic constructs that EVPN uses for Layer-2 services (or Layer-2
   Virtual Networks):

   *  BD1 is an EVPN Broadcast Domain for a given tenant and TS1, TS2
      and TS3 are connected to it.  The five represented NVEs are
      attached to BD1 and are connected to the same underlay IP network.
      That is, each NVE learns the remote NVEs' loopback addresses via
      underlay routing protocol.

   *  NVE1 is deployed as a virtual switch in a Hypervisor with IP-A as
      underlay loopback IP address.  The rest of the NVEs in Figure 1
      are physical switches and TS2/TS3 are multi-homed to them.  TS1 is
      a virtual machine, identified by MAC1 and IP1.  TS2 and TS3 are
      physically dual-connected to NVEs, hence they are normally not
      considered virtual machines.

4.2.1.  Auto-Discovery and Auto-Provisioning

   Auto-discovery is one of the basic capabilities of EVPN.  The
   provisioning of EVPN components in NVEs is significantly automated,
   simplifying the deployment of services and minimizing manual
   operations that are prone to human error.



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   These are some of the Auto-Discovery and Auto-Provisioning
   capabilities available in EVPN:

   *  Automation on Ethernet Segments (ES): an ES is defined as a group
      of NVEs that are attached to the same TS or network.  An ES is
      identified by an Ethernet Segment Identifier (ESI) in the control
      plane, but neither the ESI nor the NVEs that share the same ES are
      required to be manually provisioned in the local NVE:

      -  If the multi-homed TS or network are running protocols such as
         LACP (Link Aggregation Control Protocol) [IEEE.802.1AX_2014],
         MSTP (Multiple-instance Spanning Tree Protocol), G.8032, etc.
         and all the NVEs in the ES can listen to the protocol PDUs to
         uniquely identify the multi-homed TS/network, then the ESI can
         be "auto-sensed" or "auto-provisioned" following the guidelines
         in [RFC7432] section 5.  The ESI can also be auto-derived out
         of other parameters that are common to all NVEs attached to the
         same ES.

      -  As described in [RFC7432], EVPN can also auto-derive the BGP
         parameters required to advertise the presence of a local ES in
         the control plane (RT and RD).  Local ESes are advertised using
         RT-4 routes and the ESI-import Route-Target used by RT-4 routes
         can be auto-derived based on the procedures of [RFC7432],
         section 7.6.

      -  By listening to other RT-4 routes that match the local ESI and
         import RT, an NVE can also auto-discover the other NVEs
         participating in the multi-homing for the ES.

      -  Once the NVE has auto-discovered all the NVEs attached to the
         same ES, the NVE can automatically perform the DF Election
         algorithm (which determines the NVE that will forward traffic
         to the multi-homed TS/network).  EVPN guarantees that all the
         NVEs in the ES have a consistent DF Election.

   *  Auto-provisioning of services: when deploying a Layer-2 Service
      for a tenant in an NVO3 network, all the NVEs attached to the same
      subnet must be configured with a MAC-VRF and the BD for the
      subnet, as well as certain parameters for them.  Note that, if the
      EVPN service model is VLAN-based or VLAN-bundle, implementations
      do not normally have a specific provisioning for the BD (since it
      is in that case the same construct as the MAC-VRF).  EVPN allows
      auto-deriving as many MAC-VRF parameters as possible.  As an
      example, the MAC-VRF's RT and RD for the EVPN routes may be auto-
      derived.  Section 5.1.2.1 in [RFC8365] specifies how to auto-
      derive a MAC-VRF's RT as long as VLAN-based service model is
      implemented.  [RFC7432] specifies how to auto-derive the RD.



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4.2.2.  Remote NVE Auto-Discovery

   Auto-discovery via MP-BGP [RFC4760] is used to discover the remote
   NVEs attached to a given BD, the NVEs participating in a given
   redundancy group, the tunnel encapsulation types supported by an NVE,
   etc.

   In particular, when a new MAC-VRF and BD are enabled, the NVE will
   advertise a new RT-3 route.  Besides other fields, the RT-3 route
   will encode the IP address of the advertising NVE, the Ethernet Tag
   (which is zero in case of VLAN-based and VLAN-bundle models) and also
   a PMSI Tunnel Attribute (PTA) that indicates the information about
   the intended way to deliver BUM traffic for the BD.

   In the example of Figure 1, when BD1 is enabled, NVE1 will send an
   RT-3 route including its own IP address, Ethernet-Tag for BD1 and the
   PTA to the remote NVEs.  Assuming Ingress Replication (IR) is used,
   the RT-3 route will include an identification for IR in the PTA and
   the VNI that the other NVEs in the BD must use to send BUM traffic to
   the advertising NVE.  The other NVEs in the BD will import the RT-3
   route and will add NVE1's IP address to the flooding list for BD1.
   Note that the RT-3 route is also sent with a BGP encapsulation
   attribute [RFC9012] that indicates what NVO3 encapsulation the remote
   NVEs should use when sending BUM traffic to NVE1.

   Refer to [RFC7432] for more information about the RT-3 route and
   forwarding of BUM traffic, and to [RFC8365] for its considerations on
   NVO3 networks.

4.2.3.  Distribution of Tenant MAC and IP Information

   Tenant MAC/IP information is advertised to remote NVEs using RT-2
   routes.  Following the example of Figure 1:

   *  In a given EVPN BD, TSes' MAC addresses are first learned at the
      NVE they are attached to, via data path or management plane
      learning.  In Figure 1 we assume NVE1 learns MAC1/IP1 in the
      management plane (for instance, via Cloud Management System) since
      the NVE is a virtual switch.  NVE2, NVE3, NVE4 and NVE5 are TOR/
      Leaf switches and they normally learn MAC addresses via data path.

   *  Once NVE1's BD1 learns MAC1/IP1, NVE1 advertises that information
      along with a VNI and Next Hop IP-A in an RT-2 route.  The EVPN
      routes are advertised using the RD/RTs of the MAC-VRF where the BD
      belongs.  All the NVEs in BD1 learn local MAC/IP addresses and
      advertise them in RT-2 routes in a similar way.





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   *  The remote NVEs can then add MAC1 to their mapping table for BD1
      (BT).  For instance, when TS3 sends frames to NVE4 with MAC DA =
      MAC1, NVE4 does a MAC lookup on the BT that yields IP-A and Label
      L.  NVE4 can then encapsulate the frame into an NVO3 tunnel with
      IP-A as the tunnel IP DA and L as the Virtual Network Identifier.
      Note that the RT-2 route may also contain the host's IP address
      (as in the example of Figure 1).  While the MAC of the received
      RT-2 route is installed in the BT, the IP address may be installed
      in the Proxy-ARP/ND table (if enabled) or in the ARP/IP-VRF tables
      if the BD has an IRB.  See Section 4.7.3 to see more information
      about Proxy-ARP/ND and Section 4.3. for more details about IRB and
      Layer-3 services.

   Refer to [RFC7432] and [RFC8365] for more information about the RT-2
   route and forwarding of known unicast traffic.

4.3.  EVPN Basic Applicability for Layer-3 Services

   [RFC9136] and [RFC9135] are the reference documents that describe how
   EVPN can be used for Layer-3 services.  Inter Subnet Forwarding in
   EVPN networks is implemented via IRB interfaces between BDs and IP-
   VRFs.  An EVPN BD corresponds to an IP subnet.  When IP packets
   generated in a BD are destined to a different subnet (different BD)
   of the same tenant, the packets are sent to the IRB attached to the
   local BD in the source NVE.  As discussed in [RFC9135], depending on
   how the IP packets are forwarded between the ingress NVE and the
   egress NVE, there are two forwarding models: Asymmetric and Symmetric
   model.

   The Asymmetric model is illustrated in the example of Figure 2 and it
   requires the configuration of all the BDs of the tenant in all the
   NVEs attached to the same tenant.  In that way, there is no need to
   advertise IP Prefixes between NVEs since all the NVEs are attached to
   all the subnets.  It is called Asymmetric because the ingress and
   egress NVEs do not perform the same number of lookups in the data
   plane.  In Figure 2, if TS1 and TS2 are in different subnets, and TS1
   sends IP packets to TS2, the following lookups are required in the
   data path: a MAC lookup (on BD1's table), an IP lookup (on the IP-
   VRF) and a MAC lookup (on BD2's table) at the ingress NVE1 and then
   only a MAC lookup at the egress NVE.  The two IP-VRFs in Figure 2 are
   not connected by tunnels and all the connectivity between the NVEs is
   done based on tunnels between the BDs.









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                  +-------------------------------------+
                  |             EVPN NVO3               |
                  |                                     |
                NVE1                                 NVE2
          +--------------------+            +--------------------+
          | +---+IRB +------+  |            |  +------+IRB +---+ |
    TS1-----|BD1|----|IP-VRF|  |            |  |IP-VRF|----|BD1| |
          | +---+    |      |  |            |  |      |    +---+ |
          | +---+    |      |  |            |  |      |    +---+ |
          | |BD2|----|      |  |            |  |      |----|BD2|----TS2
          | +---+IRB +------+  |            |  +------+IRB +---+ |
          +--------------------+            +--------------------+
                  |                                     |
                  +-------------------------------------+

        Figure 2: EVPN for L3 in an NVO3 Network - Asymmetric model

   In the Symmetric model, depicted in Figure 3, the same number of data
   path lookups is needed at the ingress and egress NVEs.  For example,
   if TS1 sends IP packets to TS3, the following data path lookups are
   required: a MAC lookup at NVE1's BD1 table, an IP lookup at NVE1's
   IP-VRF and then IP lookup and MAC lookup at NVE2's IP-VRF and BD3
   respectively.  In the Symmetric model, the Inter Subnet connectivity
   between NVEs is done based on tunnels between the IP-VRFs.

                  +-------------------------------------+
                  |             EVPN NVO3               |
                  |                                     |
                NVE1                                 NVE2
          +--------------------+            +--------------------+
          | +---+IRB +------+  |            |  +------+IRB +---+ |
    TS1-----|BD1|----|IP-VRF|  |            |  |IP-VRF|----|BD3|-----TS3
          | +---+    |      |  |            |  |      |    +---+ |
          | +---+IRB |      |  |            |  +------+          |
    TS2-----|BD2|----|      |  |            +--------------------+
          | +---+    +------+  |                        |
          +--------------------+                        |
                  |                                     |
                  +-------------------------------------+

         Figure 3: EVPN for L3 in an NVO3 Network - Symmetric model

   The Symmetric model scales better than the Asymmetric model because
   it does not require the NVEs to be attached to all the tenant's
   subnets.  However, it requires the use of NVO3 tunnels on the IP-VRFs
   and the exchange of IP Prefixes between the NVEs in the control
   plane.  EVPN uses RT-2 and RT-5 routes for the exchange of host IP
   routes (in the case of the RT-2 and the RT-5 routes) and IP Prefixes



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   (RT-5 routes) of any length.  As an example, in Figure 3, NVE2 needs
   to advertise TS3's host route and/or TS3's subnet, so that the IP
   lookup on NVE1's IP- VRF succeeds.

   [RFC9135] specifies the use of RT-2 routes for the advertisement of
   host routes.  Section 4.4.1 in [RFC9136] specifies the use of RT-5
   routes for the advertisement of IP Prefixes in an "Interface-less IP-
   VRF-to-IP-VRF Model".  The Symmetric model for host routes can be
   implemented following either approach:

   a.  [RFC9135] uses RT-2 routes to convey the information to populate
       L2, ARP/ND and L3 FIB tables in the remote NVE.  For instance, in
       Figure 3, NVE2 would advertise a RT-2 route with TS3's IP and MAC
       addresses, and including two labels/VNIs: a label-3/VNI-3 that
       identifies BD3 for MAC lookup (that would be used for L2 traffic
       in case NVE1 was attached to BD3 too) and a label-1/VNI-1 that
       identifies the IP-VRF for IP lookup (and will be used for L3
       traffic).  NVE1 imports the RT-2 route and installs TS3's IP in
       the IP-VRF route table with label-1/VNI-1.  Traffic from e.g.,
       TS2 to TS3, will be encapsulated with label-1/VNI-1 and forwarded
       to NVE2.

   b.  [RFC9136] uses RT-2 routes to convey the information to populate
       the L2 FIB and ARP/ND tables, and RT-5 routes to populate the IP-
       VRF L3 FIB table.  For instance, in Figure 3, NVE2 would
       advertise a RT-2 route including TS3's MAC and IP addresses with
       a single label-3/VNI-3.  In this example, this RT-2 route
       wouldn't be imported by NVE1 because NVE1 is not attached to BD3.
       In addition, NVE2 would advertise a RT-5 route with TS3's IP
       address and label-1/VNI-1.  This RT-5 route would be imported by
       NVE1's IP-VRF and the host route installed in the L3 FIB
       associated to label-1/VNI-1.  Traffic from TS2 to TS3 would be
       encapsulated with label-1/VNI-1.

4.4.  EVPN as Control Plane for NVO3 Encapsulations and GENEVE

   [RFC8365] describes how to use EVPN for NVO3 encapsulations, such us
   VXLAN, nvGRE or MPLSoGRE.  The procedures can be easily applicable to
   any other NVO3 encapsulation, in particular GENEVE.

   The Generic Network Virtualization Encapsulation [RFC8926] has been
   recommended to be the proposed standard for NVO3 Encapsulation.  The
   EVPN control plane can signal the GENEVE encapsulation type in the
   BGP Tunnel Encapsulation Extended Community (see [RFC9012]).

   The NVO3 encapsulation design team has made a recommendation in
   [I-D.ietf-nvo3-encap] for a control plane to:




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   1.  Negotiate a subset of GENEVE option TLVs that can be carried on a
       GENEVE tunnel

   2.  Enforce an order for GENEVE option TLVs and

   3.  Limit the total number of options that could be carried on a
       GENEVE tunnel.

   The EVPN control plane can easily extend the BGP Tunnel Encapsulation
   Attribute sub-TLV [RFC9012] to specify the GENEVE tunnel options that
   can be received or transmitted over a GENEVE tunnels by a given NVE.
   [I-D.ietf-bess-evpn-geneve] describes the EVPN control plane
   extensions to support GENEVE.

4.5.  EVPN OAM and Application to NVO3

   EVPN OAM (as in [I-D.ietf-bess-evpn-lsp-ping]) defines mechanisms to
   detect data plane failures in an EVPN deployment over an MPLS
   network.  These mechanisms detect failures related to P2P and P2MP
   connectivity, for multi-tenant unicast and multicast L2 traffic,
   between multi-tenant access nodes connected to EVPN PE(s), and in a
   single-homed, single-active or all-active redundancy model.

   In general, EVPN OAM mechanisms defined for EVPN deployed in MPLS
   networks are equally applicable for EVPN in NVO3 networks.

4.6.  EVPN as the Control Plane for NVO3 Security

   EVPN can be used to signal the security protection capabilities of a
   sender NVE, as well as what portion of an NVO3 packet (taking a
   GENEVE packet as an example) can be protected by the sender NVE, to
   ensure the privacy and integrity of tenant traffic carried over the
   NVO3 tunnels [I-D.sajassi-bess-secure-evpn].

4.7.  Advanced EVPN Features for NVO3 Networks

   This section describes how EVPN can be used to deliver advanced
   capabilities in NVO3 networks.

4.7.1.  Virtual Machine (VM) Mobility

   [RFC7432] replaces the traditional Ethernet Flood-and-Learn behavior
   among NVEs with BGP-based MAC learning, which in return provides more
   control over the location of MAC addresses in the BD and consequently
   advanced features, such as MAC Mobility.  If we assume that VM
   Mobility means the VM's MAC and IP addresses move with the VM, EVPN's
   MAC Mobility is the required procedure that facilitates VM Mobility.
   According to [RFC7432] section 15, when a MAC is advertised for the



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   first time in a BD, all the NVEs attached to the BD will store
   Sequence Number zero for that MAC.  When the MAC "moves" within the
   same BD but to a remote NVE, the NVE that just learned locally the
   MAC, increases the Sequence Number in the RT-2 route's MAC Mobility
   extended community to indicate that it owns the MAC now.  That makes
   all the NVE in the BD change their tables immediately with no need to
   wait for any aging timer.  EVPN guarantees a fast MAC Mobility
   without flooding or black-holes in the BD.

4.7.2.  MAC Protection, Duplication Detection and Loop Protection

   The advertisement of MACs in the control plane, allows advanced
   features such as MAC protection, Duplication Detection and Loop
   Protection.

   [RFC7432] MAC Protection refers to EVPN's ability to indicate - in a
   RT-2 route - that a MAC must be protected by the NVE receiving the
   route.  The Protection is indicated in the "Sticky bit" of the MAC
   Mobility extended community sent along the RT-2 route for a MAC.
   NVEs' ACs that are connected to subject-to-be-protected servers or
   VMs, may set the Sticky bit on the RT-2 routes sent for the MACs
   associated to the ACs.  Also, statically configured MAC addresses
   should be advertised as Protected MAC addresses, since they are not
   subject to MAC Mobility procedures.

   [RFC7432] MAC Duplication Detection refers to EVPN's ability to
   detect duplicate MAC addresses.  A "MAC move" is a relearn event that
   happens at an access AC or through a RT-2 route with a Sequence
   Number that is higher than the stored one for the MAC.  When a MAC
   moves a number of times N within an M-second window between two NVEs,
   the MAC is declared as Duplicate and the detecting NVE does not re-
   advertise the MAC anymore.

   [RFC7432] provides MAC Duplication Detection, and with an extension
   it can protect the BD against loops created by backdoor links between
   NVEs.  The same principle (based on the Sequence Number) may be
   extended to protect the BD against loops.  When a MAC is detected as
   duplicate, the NVE may install it as a black-hole MAC and drop
   received frames with MAC SA and MAC DA matching that duplicate MAC.
   The MAC Duplication extension to support Loop Protection is described
   in [I-D.ietf-bess-rfc7432bis].

4.7.3.  Reduction/Optimization of BUM Traffic in Layer-2 Services

   In BDs with a significant amount of flooding due to Unknown unicast
   and Broadcast frames, EVPN may help reduce and sometimes even
   suppress the flooding.




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   In BDs where most of the Broadcast traffic is caused by ARP (Address
   Resolution Protocol) and ND (Neighbor Discovery) protocols on the
   TSes, EVPN's Proxy-ARP and Proxy-ND capabilities may reduce the
   flooding drastically.  The use of Proxy-ARP/ND is specified in
   [RFC9161].

   Proxy-ARP/ND procedures along with the assumption that TSes always
   issue a GARP (Gratuitous ARP) or an unsolicited Neighbor
   Advertisement message when they come up in the BD, may drastically
   reduce the unknown unicast flooding in the BD.

   The flooding caused by TSes' IGMP/MLD or PIM messages in the BD may
   also be suppressed by the use of IGMP/MLD and PIM Proxy functions, as
   specified in [I-D.ietf-bess-evpn-igmp-mld-proxy] and
   [I-D.skr-bess-evpn-pim-proxy].  These two documents also specify how
   to forward IP multicast traffic efficiently within the same BD,
   translate soft state IGMP/MLD/PIM messages into hard state BGP routes
   and provide fast-convergence redundancy for IP Multicast on multi-
   homed Ethernet Segments (ESes).

4.7.4.  Ingress Replication (IR) Optimization for BUM Traffic

   When an NVE attached to a given BD needs to send BUM traffic for the
   BD to the remote NVEs attached to the same BD, Ingress Replication is
   a very common option in NVO3 networks, since it is completely
   independent of the multicast capabilities of the underlay network.
   Also, if the optimization procedures to reduce/suppress the flooding
   in the BD are enabled (Section 4.7.3), in spite of creating multiple
   copies of the same frame at the ingress NVE, Ingress Replication may
   be good enough.  However, in BDs where Multicast (or Broadcast)
   traffic is significant, Ingress Replication may be very inefficient
   and cause performance issues on virtual-switch-based NVEs.

   [I-D.ietf-bess-evpn-optimized-ir] specifies the use of AR (Assisted
   Replication) NVO3 tunnels in EVPN BDs.  AR retains the independence
   of the underlay network while providing a way to forward Broadcast
   and Multicast traffic efficiently.  AR uses AR-REPLICATORs that can
   replicate the Broadcast/Multicast traffic on behalf of the AR-LEAF
   NVEs.  The AR-LEAF NVEs are typically virtual-switches or NVEs with
   limited replication capabilities.  AR can work in a single-stage
   replication mode (Non-Selective Mode) or in a dual-stage replication
   mode (Selective Mode).  Both modes are detailed in
   [I-D.ietf-bess-evpn-optimized-ir].

   In addition, [I-D.ietf-bess-evpn-optimized-ir] also describes a
   procedure to avoid sending Broadcast, Multicast or Unknown unicast to
   certain NVEs that do not need that type of traffic.  This is done by
   enabling PFL (Pruned Flood Lists) on a given BD.  For instance, an



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   virtual-switch NVE that learns all its local MAC addresses for a BD
   via Cloud Management System, does not need to receive the BD's
   Unknown unicast traffic.  Pruned Flood Lists help optimize the BUM
   flooding in the BD.

4.7.5.  EVPN Multi-Homing

   Another fundamental concept in EVPN is multi-homing.  A given TS can
   be multi-homed to two or more NVEs for a given BD, and the set of
   links connected to the same TS is defined as Ethernet Segment (ES).
   EVPN supports single-active and all-active multi-homing.  In single-
   active multi-homing only one link in the ES is active.  In all-active
   multi-homing all the links in the ES are active for unicast traffic.
   Both modes support load-balancing:

   *  Single-active multi-homing means per-service load-balancing to/
      from the TS.  For example, in Figure 1, for BD1, only one of the
      NVEs can forward traffic from/to TS2.  For a different BD, the
      other NVE may forward traffic.

   *  All-active multi-homing means per-flow load-balanding for unicast
      frames to/from the TS.  That is, in Figure 1 and for BD1, both
      NVE4 and NVE5 can forward known unicast traffic to/from TS3.  For
      BUM traffic only one of the two NVEs can forward traffic to TS3,
      and both can forward traffic from TS3.

   There are two key aspects in the EVPN multi-homing procedures:

   *  DF (Designated Forwarder) election: the DF is the NVE that
      forwards the traffic to the ES in single-active mode.  In case of
      all-active, the DF is the NVE that forwards the BUM traffic to the
      ES.

   *  Split-horizon function: prevents the TS from receiving echoed BUM
      frames that the TS itself sent to the ES.  This is especially
      relevant in all-active ESes, where the TS may forward BUM frames
      to a non-DF NVE that can flood the BUM frames back to the DF NVE
      and then the TS.  As an example, in Figure 1, assuming NVE4 is the
      DF for ES-2 in BD1, BUM frames sent from TS3 to NVE5 will be
      received at NVE4 and, since NVE4 is the DF for DB1, it will
      forward them back to TS3.  Split-horizon allows NVE4 (and any
      multi-homed NVE for that matter) to identify if an EVPN BUM frame
      is coming from the same ES or different, and if the frame belongs
      to the same ES2, NVE4 will not forward the BUM frame to TS3, in
      spite of being the DF.






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   While [RFC7432] describes the default algorithm for the DF Election,
   [RFC8584] and [I-D.ietf-bess-evpn-pref-df] specify other algorithms
   and procedures that optimize the DF Election.

   The Split-horizon function is specified in [RFC7432] and it is
   carried out by using a special ESI-label that it identifies in the
   data path, all the BUM frames being originated from a given NVE and
   ES.  Since the ESI-label is an MPLS label, it cannot be used in all
   the non-MPLS NVO3 encapsulations, therefore [RFC8365] defines a
   modified Split-horizon procedure that is based on the IP SA of the
   NVO3 tunnel, and it is known as "Local-Bias".  It is worth noting
   that Local-Bias only works for all-active multi-homing, and not for
   single-active multi-homing.

4.7.6.  EVPN Recursive Resolution for Inter-Subnet Unicast Forwarding

   Section 4.3 describes how EVPN can be used for Inter Subnet
   Forwarding among subnets of the same tenant.  RT-2 routes and RT-5
   routes allow the advertisement of host routes and IP Prefixes (RT-5
   route) of any length.  The procedures outlined by Section 4.3 are
   similar to the ones in [RFC4364], only for NVO3 tunnels.  However,
   [RFC9136] also defines advanced Inter Subnet Forwarding procedures
   that allow the resolution of RT-5 routes to not only BGP next-hops
   but also "overlay indexes" that can be a MAC, a GW IP or an ESI, all
   of them in the tenant space.

   Figure 4 illustrates an example that uses Recursive Resolution to a
   GW-IP as per [RFC9136] section 4.4.2.  In this example, IP-VRFs in
   NVE1 and NVE2 are connected by a SBD (Supplementary BD).  An SBD is a
   BD that connects all the IP-VRFs of the same tenant, via IRB, and has
   no ACs.  NVE1 advertises the host route TS2-IP/L (IP address and
   Prefix Length of TS2) in an RT-5 route with overlay index GWIP=IP1.
   Also, IP1 is advertised in an RT-2 route associated to M1, VNI-S and
   BGP next-hop NVE1.  Upon importing the two routes, NVE2 installs TS2-
   IP/L in the IP-VRF with a next-hop that is the GWIP IP1.  NVE2 also
   installs M1 in the SBD, with VNI-S and NVE1 as next-hop.  If TS3
   sends a packet with IP DA=TS2, NVE2 will perform a Recursive
   Resolution of the RT-5 route prefix information to the forwarding
   information of the correlated RT-2 route.  The RT-5 route's Recursive
   Resolution has several advantages such as better convergence in
   scaled networks (since multiple RT-5 routes can be invalidated with a
   single withdrawal of the overlay index route) or the ability to
   advertise multiple RT-5 routes from an overlay index that can move or
   change dynamically.  [RFC9136] describes a few use-cases.







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                  +-------------------------------------+
                  |             EVPN NVO3               |
                  |                                     +
                NVE1                                 NVE2
          +--------------------+            +--------------------+
          | +---+IRB +------+  |            |  +------+IRB +---+ |
    TS1-----|BD1|----|IP-VRF|  |            |  |IP-VRF|----|BD3|-----TS3
          | +---+    |      |-(SBD)------(SBD)-|      |    +---+ |
          | +---+IRB |      |IRB(IP1/M1)    IRB+------+          |
    TS2-----|BD2|----|      |  |            +-----------+--------+
          | +---+    +------+  |                        |
          +--------------------+                        |
                  |   RT-2(M1,IP1,VNI-S,NVE1)-->        |
                  |     RT-5(TS2-IP/L,GWIP=IP1)-->      |
                  +-------------------------------------+

            Figure 4: EVPN for L3 - Recursive Resolution example

4.7.7.  EVPN Optimized Inter-Subnet Multicast Forwarding

   The concept of the SBD described in Section 4.7.6 is also used in
   [I-D.ietf-bess-evpn-irb-mcast] for the procedures related to Inter
   Subnet Multicast Forwarding across BDs of the same tenant.  For
   instance, [I-D.ietf-bess-evpn-irb-mcast] allows the efficient
   forwarding of IP multicast traffic from any BD to any other BD (or
   even to the same BD where the Source resides).  The
   [I-D.ietf-bess-evpn-irb-mcast] procedures are supported along with
   EVPN multi-homing, and for any tree allowed on NVO3 networks,
   including IR or AR.  [I-D.ietf-bess-evpn-irb-mcast] also describes
   the interoperability between EVPN and other multicast technologies
   such as MVPN (Multicast VPN) and PIM for inter-subnet multicast.

   [I-D.ietf-bess-evpn-mvpn-seamless-interop] describes another
   potential solution to support EVPN to MVPN interoperability.

4.7.8.  Data Center Interconnect (DCI)

   Tenant Layer-2 and Layer-3 services deployed on NVO3 networks must be
   extended to remote NVO3 networks that are connected via non-NOV3 WAN
   networks (mostly MPLS based WAN networks).  [RFC9014] defines some
   architectural models that can be used to interconnect NVO3 networks
   via MPLS WAN networks.









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   When NVO3 networks are connected by MPLS WAN networks, [RFC9014]
   specifies how EVPN can be used end-to-end, in spite of using a
   different encapsulation in the WAN.  [RFC9014] also supports the use
   of NVO3 or Segment Routing (encoding 32-bit or 128-bit Segment
   Identifiers into labels or IPv6 addresses respectively) transport
   tunnels in the WAN.

   Even if EVPN can also be used in the WAN for Layer-2 and Layer-3
   services, there may be a need to provide a Gateway function between
   EVPN for NVO3 encapsulations and IPVPN for MPLS tunnels, if the
   operator uses IPVPN in the WAN.
   [I-D.ietf-bess-evpn-ipvpn-interworking] specifies the interworking
   function between EVPN and IPVPN for unicast Inter Subnet Forwarding.
   If Inter Subnet Multicast Forwarding is also needed across an IPVPN
   WAN, [I-D.ietf-bess-evpn-irb-mcast] describes the required
   interworking between EVPN and MVPN (Multicast Virtual Private
   Networks).

5.  Conclusion

   EVPN provides a unified control-plane that solves the NVE auto-
   discovery, tenant MAP/IP dissemination and advanced features required
   by NVO3 networks, in a scalable way and keeping the independence of
   the underlay IP Fabric, i.e. there is no need to enable PIM in the
   underlay network and maintain multicast states for tenant BDs.

   This document justifies the use of EVPN for NVO3 networks, discusses
   its applicability to basic Layer-2 and Layer-3 connectivity
   requirements, as well as advanced features such as MAC-mobility, MAC
   Protection and Loop Protection, multi-homing, DCI and much more.

6.  Conventions Used in this Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

7.  Security Considerations

   This document does not introduce any new procedure or additional
   signaling in EVPN, and relies on the security considerations of the
   individual specifications used as a reference throughout the
   document.  In particular, and as mentioned in [RFC7432], control
   plane and forwarding path protection are aspects to secure in any
   EVPN domain, when applied to NVO3 networks.




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   [RFC7432] mentions security techniques such as those discussed in
   [RFC5925] to authenticate BGP messages, and those included in
   [RFC4271], [RFC4272] and [RFC6952] to secure BGP are relevant for
   EVPN in NVO3 networks as well.

8.  IANA Considerations

   None.

9.  References

9.1.  Normative References

   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
              Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
              Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
              2015, <https://www.rfc-editor.org/info/rfc7432>.

   [RFC7365]  Lasserre, M., Balus, F., Morin, T., Bitar, N., and Y.
              Rekhter, "Framework for Data Center (DC) Network
              Virtualization", RFC 7365, DOI 10.17487/RFC7365, October
              2014, <https://www.rfc-editor.org/info/rfc7365>.

   [RFC7364]  Narten, T., Ed., Gray, E., Ed., Black, D., Fang, L.,
              Kreeger, L., and M. Napierala, "Problem Statement:
              Overlays for Network Virtualization", RFC 7364,
              DOI 10.17487/RFC7364, October 2014,
              <https://www.rfc-editor.org/info/rfc7364>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

9.2.  Informative References

   [RFC9136]  Rabadan, J., Ed., Henderickx, W., Drake, J., Lin, W., and
              A. Sajassi, "IP Prefix Advertisement in Ethernet VPN
              (EVPN)", RFC 9136, DOI 10.17487/RFC9136, October 2021,
              <https://www.rfc-editor.org/info/rfc9136>.







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   [RFC9135]  Sajassi, A., Salam, S., Thoria, S., Drake, J., and J.
              Rabadan, "Integrated Routing and Bridging in Ethernet VPN
              (EVPN)", RFC 9135, DOI 10.17487/RFC9135, October 2021,
              <https://www.rfc-editor.org/info/rfc9135>.

   [RFC8365]  Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R.,
              Uttaro, J., and W. Henderickx, "A Network Virtualization
              Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365,
              DOI 10.17487/RFC8365, March 2018,
              <https://www.rfc-editor.org/info/rfc8365>.

   [RFC8926]  Gross, J., Ed., Ganga, I., Ed., and T. Sridhar, Ed.,
              "Geneve: Generic Network Virtualization Encapsulation",
              RFC 8926, DOI 10.17487/RFC8926, November 2020,
              <https://www.rfc-editor.org/info/rfc8926>.

   [I-D.ietf-nvo3-encap]
              Boutros, S. and D. E. Eastlake, "Network Virtualization
              Overlays (NVO3) Encapsulation Considerations", Work in
              Progress, Internet-Draft, draft-ietf-nvo3-encap-08, 30
              April 2022, <https://www.ietf.org/archive/id/draft-ietf-
              nvo3-encap-08.txt>.

   [RFC9012]  Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
              "The BGP Tunnel Encapsulation Attribute", RFC 9012,
              DOI 10.17487/RFC9012, April 2021,
              <https://www.rfc-editor.org/info/rfc9012>.

   [I-D.ietf-bess-evpn-lsp-ping]
              Jain, P., Salam, S., Sajassi, A., Boutros, S., and G.
              Mirsky, "LSP-Ping Mechanisms for EVPN and PBB-EVPN", Work
              in Progress, Internet-Draft, draft-ietf-bess-evpn-lsp-
              ping-07, 10 February 2022,
              <https://www.ietf.org/archive/id/draft-ietf-bess-evpn-lsp-
              ping-07.txt>.

   [RFC9161]  Rabadan, J., Ed., Sathappan, S., Nagaraj, K., Hankins, G.,
              and T. King, "Operational Aspects of Proxy ARP/ND in
              Ethernet Virtual Private Networks", RFC 9161,
              DOI 10.17487/RFC9161, January 2022,
              <https://www.rfc-editor.org/info/rfc9161>.

   [I-D.ietf-bess-evpn-igmp-mld-proxy]
              Sajassi, A., Thoria, S., Mishra, M., Drake, J., and W.
              Lin, "IGMP and MLD Proxy for EVPN", Work in Progress,
              Internet-Draft, draft-ietf-bess-evpn-igmp-mld-proxy-21, 22
              March 2022, <https://www.ietf.org/archive/id/draft-ietf-
              bess-evpn-igmp-mld-proxy-21.txt>.



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   [I-D.skr-bess-evpn-pim-proxy]
              Rabadan, J., Kotalwar, J., Sathappan, S., Zhang, Z., and
              A. Sajassi, "PIM Proxy in EVPN Networks", Work in
              Progress, Internet-Draft, draft-skr-bess-evpn-pim-proxy-
              01, 30 October 2017, <https://www.ietf.org/archive/id/
              draft-skr-bess-evpn-pim-proxy-01.txt>.

   [I-D.ietf-bess-evpn-optimized-ir]
              Rabadan, J., Sathappan, S., Lin, W., Katiyar, M., and A.
              Sajassi, "Optimized Ingress Replication Solution for
              Ethernet VPN (EVPN)", Work in Progress, Internet-Draft,
              draft-ietf-bess-evpn-optimized-ir-12, 25 January 2022,
              <https://www.ietf.org/archive/id/draft-ietf-bess-evpn-
              optimized-ir-12.txt>.

   [RFC8584]  Rabadan, J., Ed., Mohanty, S., Ed., Sajassi, A., Drake,
              J., Nagaraj, K., and S. Sathappan, "Framework for Ethernet
              VPN Designated Forwarder Election Extensibility",
              RFC 8584, DOI 10.17487/RFC8584, April 2019,
              <https://www.rfc-editor.org/info/rfc8584>.

   [I-D.ietf-bess-evpn-pref-df]
              Rabadan, J., Sathappan, S., Przygienda, T., Lin, W.,
              Drake, J., Sajassi, A., and S. Mohanty, "Preference-based
              EVPN DF Election", Work in Progress, Internet-Draft,
              draft-ietf-bess-evpn-pref-df-08, 23 September 2021,
              <https://www.ietf.org/archive/id/draft-ietf-bess-evpn-
              pref-df-08.txt>.

   [I-D.ietf-bess-evpn-irb-mcast]
              Lin, W., Zhang, Z., Drake, J., Rosen, E. C., Rabadan, J.,
              and A. Sajassi, "EVPN Optimized Inter-Subnet Multicast
              (OISM) Forwarding", Work in Progress, Internet-Draft,
              draft-ietf-bess-evpn-irb-mcast-06, 24 May 2021,
              <https://www.ietf.org/archive/id/draft-ietf-bess-evpn-irb-
              mcast-06.txt>.

   [RFC9014]  Rabadan, J., Ed., Sathappan, S., Henderickx, W., Sajassi,
              A., and J. Drake, "Interconnect Solution for Ethernet VPN
              (EVPN) Overlay Networks", RFC 9014, DOI 10.17487/RFC9014,
              May 2021, <https://www.rfc-editor.org/info/rfc9014>.










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   [I-D.ietf-bess-evpn-ipvpn-interworking]
              Rabadan, J., Sajassi, A., Rosen, E., Drake, J., Lin, W.,
              Uttaro, J., and A. Simpson, "EVPN Interworking with
              IPVPN", Work in Progress, Internet-Draft, draft-ietf-bess-
              evpn-ipvpn-interworking-06, 22 September 2021,
              <https://www.ietf.org/archive/id/draft-ietf-bess-evpn-
              ipvpn-interworking-06.txt>.

   [RFC7348]  Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
              L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
              eXtensible Local Area Network (VXLAN): A Framework for
              Overlaying Virtualized Layer 2 Networks over Layer 3
              Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
              <https://www.rfc-editor.org/info/rfc7348>.

   [RFC7510]  Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black,
              "Encapsulating MPLS in UDP", RFC 7510,
              DOI 10.17487/RFC7510, April 2015,
              <https://www.rfc-editor.org/info/rfc7510>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [CLOS1953] Clos, C., "A Study of Non-Blocking Switching Networks",
              March 1953.

   [I-D.ietf-bess-evpn-geneve]
              Boutros, S., Sajassi, A., Drake, J., Rabadan, J., and S.
              Aldrin, "EVPN control plane for Geneve", Work in Progress,
              Internet-Draft, draft-ietf-bess-evpn-geneve-04, 23 May
              2022, <https://www.ietf.org/archive/id/draft-ietf-bess-
              evpn-geneve-04.txt>.

   [I-D.ietf-bess-evpn-mvpn-seamless-interop]
              Sajassi, A., Thiruvenkatasamy, K., Thoria, S., Gupta, A.,
              and L. Jalil, "Seamless Multicast Interoperability between
              EVPN and MVPN PEs", Work in Progress, Internet-Draft,
              draft-ietf-bess-evpn-mvpn-seamless-interop-03, 25 October
              2021, <https://www.ietf.org/archive/id/draft-ietf-bess-
              evpn-mvpn-seamless-interop-03.txt>.

   [I-D.sajassi-bess-secure-evpn]
              Sajassi, A., Banerjee, A., Thoria, S., Carrel, D., Weis,
              B., and J. Drake, "Secure EVPN", Work in Progress,
              Internet-Draft, draft-sajassi-bess-secure-evpn-05, 25
              October 2021, <https://www.ietf.org/archive/id/draft-
              sajassi-bess-secure-evpn-05.txt>.



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   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC4272]  Murphy, S., "BGP Security Vulnerabilities Analysis",
              RFC 4272, DOI 10.17487/RFC4272, January 2006,
              <https://www.rfc-editor.org/info/rfc4272>.

   [RFC6952]  Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
              BGP, LDP, PCEP, and MSDP Issues According to the Keying
              and Authentication for Routing Protocols (KARP) Design
              Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
              <https://www.rfc-editor.org/info/rfc6952>.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,
              <https://www.rfc-editor.org/info/rfc4760>.

   [I-D.ietf-bess-rfc7432bis]
              Sajassi, A., Burdet, L. A., Drake, J., and J. Rabadan,
              "BGP MPLS-Based Ethernet VPN", Work in Progress, Internet-
              Draft, draft-ietf-bess-rfc7432bis-04, 7 March 2022,
              <https://www.ietf.org/archive/id/draft-ietf-bess-
              rfc7432bis-04.txt>.

   [IEEE.802.1AX_2014]
              IEEE, "IEEE Standard for Local and metropolitan area
              networks -- Link Aggregation", 24 December 2014.

Appendix A.  Acknowledgments

   The authors want to thank Aldrin Isaac for his comments.

Appendix B.  Contributors

Appendix C.  Authors' Addresses

Authors' Addresses







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   Jorge Rabadan (editor)
   Nokia
   520 Almanor Ave
   Sunnyvale, CA 94085
   United States of America
   Email: jorge.rabadan@nokia.com


   Matthew Bocci
   Nokia
   Email: matthew.bocci@nokia.com


   Sami Boutros
   Ciena
   Email: sboutros@ciena.com


   Ali Sajassi
   Cisco Systems, Inc.
   Email: sajassi@cisco.com






























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